Disk drive calibrating radial density then adjusting linear density to balance off-track read capability

1. A disk drive comprising:

a plurality of disk surfaces;

a head actuated over each disk surface; and

control circuitry operable to:

measure an off-track read capability (OTRC) for each disk surface;

select a radial density of data tracks for each disk surface in response to the OTRCs; and

after selecting the radial density of data tracks for each disk surface, adjust a linear density of at least two disk surfaces to balance the OTRCs across the disk surfaces.

2. The disk drive as recited in claim 1 , wherein the control circuitry is operable to select the radial density for each disk surface that maximizes the OTRC.

3. The disk drive as recited in claim 1 , wherein the control circuitry is operable to balance the OTRCs by:

increasing the linear density of a first disk surface to decrease the OTRC of the first disk surface; and

decreasing the linear density of a second disk surface to increase the OTRC of the second disk surface.

4. The disk drive as recited in claim 1 , wherein the control circuitry is operable to:

measure a middle diameter (MD) OTRC for each disk surface;

select a MD radial density near a middle diameter of each disk surface based on the MD OTRC;

adjust a linear density of at least two disk surfaces to balance the MD OTRCs across the disk surfaces;

measure a profile OTRC for a plurality of profile radial densities spanning each disk surface;

select one of the profile radial densities for each disk surface in response to the profile OTRCs; and

adjust the linear density of at least two disk surfaces to balance the profile OTRCs across the disk surfaces.

5. The disk drive as recited in claim 4 , wherein the control circuitry is operable to select the profile radial density for a first disk surface by:

measuring a first OTRC at an inner diameter of the first disk surface for a first profile radial density;

measuring a second OTRC at an outer diameter of the first disk surface for the first profile radial density; and

averaging the first and second OTRC to generate a first average OTRC.

6. The disk drive as recited in claim 5 , wherein the control circuitry is operable to select the profile radial density for the first disk surface by:

measuring a third OTRC at an inner diameter of the first disk surface for a second profile radial density;

measuring a fourth OTRC at an outer diameter of the first disk surface for the second profile radial density;

averaging the third and fourth OTRC to generate a second average OTRC; and

selecting between the first and second profile radial density in response to the first and second average OTRC.

7. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to reduce a combined target capacity of the disk surfaces when the balanced OTRCs falls below a threshold.

8. A method of operating a disk drive, the disk drive comprising a plurality of disk surfaces, and a head actuated over each disk surface, the method comprising:

measuring an off-track read capability (OTRC) for each disk surface;

selecting a radial density of data tracks for each disk surface in response to the OTRCs; and

after selecting the radial density of data tracks for each disk surface, adjusting a linear density of at least two disk surfaces to balance the OTRCs across the disk surfaces.

9. The method as recited in claim 8 , further comprising selecting the radial density for each disk surface that maximizes the OTRC.

10. The method as recited in claim 8 , further comprising balancing the OTRCs by:

increasing the linear density of a first disk surface to decrease the OTRC of the first disk surface; and

decreasing the linear density of a second disk surface to increase the OTRC of the second disk surface.

11. The method as recited in claim 8 , further comprising:

measuring a middle diameter (MD) OTRC for each disk surface;

selecting a MD radial density near a middle diameter of each disk surface based on the MD OTRC;

adjusting a linear density of at least two disk surfaces to balance the MD OTRCs across the disk surfaces;

measuring a profile OTRC for a plurality of profile radial densities spanning each disk surface;

selecting one of the profile radial densities for each disk surface in response to the profile OTRCs; and

adjusting the linear density of at least two disk surfaces to balance the profile OTRCs across the disk surfaces.

12. The method as recited in claim 11 , further comprising selecting the profile radial density for a first disk surface by:

measuring a first OTRC at an inner diameter of the first disk surface for a first profile radial density;

measuring a second OTRC at an outer diameter of the first disk surface for the first profile radial density; and

averaging the first and second OTRC to generate a first average OTRC.

13. The method as recited in claim 12 , further comprising selecting the profile radial density for the first disk surface by:

measuring a third OTRC at an inner diameter of the first disk surface for a second profile radial density;

measuring a fourth OTRC at an outer diameter of the first disk surface for the second profile radial density;

averaging the third and fourth OTRC to generate a second average OTRC; and

selecting between the first and second profile radial density in response to the first and second average OTRC.

14. The method as recited in claim 8 , further comprising reducing a combined target capacity of the disk surfaces when the balanced OTRCs falls below a threshold.